Methods of manufacture of bottom port surface mount MEMS microphones

ABSTRACT

Methods for manufacturing multiple bottom port, surface mount microphones, each containing a micro-electro-mechanical system (MEMS) microphone die, are disclosed. Each surface mount microphone features a substrate with metal pads for surface mounting the package to a device&#39;s printed circuit board and for making electrical connections between the microphone package and the device&#39;s circuit board. The surface mount microphones are manufactured from a panel of unsingulated substrates, each substrate having an acoustic port, and each MEMS microphone die is substrate-mounted and acoustically coupled to its respective acoustic port. Individual covers are joined to the panel of unsingulated substrates, and each individual substrate and cover pair cooperates to form an acoustic chamber for its respective MEMS microphone die. The completed panel is singulated to form individual MEMS microphones.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/839,119 (now U.S. Pat. No. 8,629,005), filed Mar. 15, 2013, which is a continuation of U.S. patent application Ser. No. 13/668,103 (now U.S. Pat. No. 8,629,551), filed Nov. 2, 2012, which is a continuation of U.S. patent application Ser. No. 13/286,558 (now U.S. Pat. No. 8,358,004), filed Nov. 1, 2011, which is a continuation of U.S. patent application Ser. No. 13/111,537 (now U.S. Pat. No. 8,121,331), filed May 19, 2011, which is a continuation of U.S. patent application Ser. No. 11/741,881 (now U.S. Pat. No. 8,018,049), filed Apr. 30, 2007, which is a divisional of U.S. patent application Ser. No. 10/921,747 (now U.S. Pat. No. 7,434,305), filed Aug. 19, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 09/886,854 (now U.S. Pat. No. 7,166,910), filed Jun. 21, 2001, which claims the benefit of U.S. Provisional Patent Application No. 60/253,543, filed Nov. 28, 2000. U.S. patent application Ser. No. 13/668,035, filed Nov. 2, 2012, U.S. patent application Ser. No. 13/668,103, filed Nov. 2, 2012, U.S. patent application Ser. No. 13/732,120, filed Dec. 31, 2012, U.S. patent application Ser. No. 13/732,179, filed Dec. 31, 2012, U.S. patent application Ser. No. 13/732,205, filed Dec. 31, 2012, and U.S. patent application Ser. No. 13/732,232, filed Dec. 31, 2012, are also continuations of U.S. patent application Ser. No. 13/286,558 (now U.S. Pat. No. 8,358,004). These applications are hereby incorporated by reference herein in their entireties for all purposes.

TECHNICAL FIELD

This patent relates generally to a housing for a transducer. More particularly, this patent relates to a silicon condenser microphone including a housing for shielding a transducer.

BACKGROUND OF THE INVENTION

There have been a number of disclosures related to building microphone elements on the surface of a silicon die. Certain of these disclosures have come in connection with the hearing aid field for the purpose of reducing the size of the hearing aid unit. While these disclosures have reduced the size of the hearing aid, they have not disclosed how to protect the transducer from outside interferences. For instance, transducers of this type are fragile and susceptible to physical damage. Furthermore, they must be protected from light and electromagnetic interferences. Moreover, they require an acoustic pressure reference to function properly. For these reasons, the silicon die must be shielded.

Some shielding practices have been used to house these devices. For instance, insulated metal cans or discs have been provided. Additionally, DIPs and small outline integrated circuit (SOIC) packages have been utilized. However, the drawbacks associated with manufacturing these housings, such as lead time, cost, and tooling, make these options undesirable.

SUMMARY OF THE INVENTION

The present invention is directed to a silicon condenser microphone package that allows acoustic energy to contact a transducer disposed within a housing. The housing provides the necessary pressure reference while at the same time protects the transducer from light, electromagnetic interference, and physical damage. In accordance with an embodiment of the invention a silicon condenser microphone includes a transducer and a substrate and a cover forming the housing. The substrate may have an upper surface with a recess formed therein allowing the transducer to be attached to the upper surface and to overlap at least a portion of the recess thus forming a back volume. The cover is placed over the transducer and includes an aperture adapted for allowing sound waves to reach the transducer.

Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a first embodiment of a silicon condenser microphone of the present invention;

FIG. 2 is a cross-sectional view of a second embodiment of a silicon condenser microphone of the present invention;

FIG. 3 is a cross-sectional view of a third embodiment of a silicon condenser microphone of the present invention;

FIG. 4 is a cross-sectional view of the third embodiment of the present invention affixed to an end user circuit board;

FIG. 5 is a cross-sectional view of the third embodiment of the present invention affixed to an end user circuit board in an alternate fashion;

FIG. 6 is a plan view of a substrate to which a silicon condenser microphone is fixed;

FIG. 7 is a longitudinal cross-sectional view of a microphone package of the present invention;

FIG. 8 is a lateral cross-sectional view of a microphone package of the present invention;

FIG. 9 is a longitudinal cross-sectional view of a microphone package of the present invention;

FIG. 10 is a lateral cross-sectional view of a microphone package of the present invention;

FIG. 11 is a cross-sectional view of a top portion for a microphone package of the present invention;

FIG. 12 is a cross-sectional view of a top portion for a microphone package of the present invention;

FIG. 13 is a cross-sectional view of a top portion for a microphone package of the present invention;

FIG. 14 a is a cross-sectional view of a laminated bottom portion of a housing for a microphone package of the present invention;

FIG. 14 b is a plan view of a layer of the laminated bottom portion of FIG. 14 a;

FIG. 14 c is a plan view of a layer of the laminated bottom portion of FIG. 14 a;

FIG. 14 d is a plan view of a layer of the laminated bottom portion of FIG. 14 a;

FIG. 15 is a cross-sectional view of a bottom portion for a microphone package of the present invention;

FIG. 16 is a cross-sectional view of a bottom portion for a microphone package of the present invention;

FIG. 17 is a cross-sectional view of a bottom portion for a microphone package of the present invention;

FIG. 18 is a cross-sectional view of a bottom portion for a microphone package of the present invention;

FIG. 19 is a plan view of a side portion for a microphone package of the present invention;

FIG. 20 is a cross-sectional view of a side portion for a microphone package of the present invention;

FIG. 21 is a cross-sectional view of a side portion for a microphone package of the present invention;

FIG. 22 is a cross-sectional view of a side portion for a microphone package of the present invention;

FIG. 23 is a cross-sectional view of a microphone package of the present invention;

FIG. 24 is a cross-sectional view of a microphone package of the present invention;

FIG. 25 is a cross-sectional view of a microphone package of the present invention;

FIG. 26 is a cross-sectional view of a microphone package of the present invention;

FIG. 27 is a cross-sectional view of a microphone package of the present invention with a retaining ring;

FIG. 28 is a cross-sectional view of a microphone package of the present invention with a retaining wing;

FIG. 29 is a cross-sectional view of a microphone package of the present invention with a retaining ring;

FIG. 30 is a plan view of a panel of a plurality of microphone packages; and

FIG. 31 is a plan view of a microphone pair.

DETAILED DESCRIPTION

While the invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail several possible embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.

The present invention is directed to microphone packages. The benefits of the microphone packages disclosed herein over microphone packaging utilizing plastic body/lead frames include the ability to process packages in panel form allowing more units to be formed per operation and at much lower cost. The typical lead frame for a similarly functioning package would contain between 40 and 100 devices connected together. The present disclosure would have approximately 14,000 devices connected together (as a panel). Also, the embodiments disclosed herein require minimal “hard-tooling” This allows the process to adjust to custom layout requirements without having to redesign mold, lead frame, and trim/form tooling.

Moreover, many of the described embodiments have a better match of thermal coefficients of expansion with the end user's PCB, typically made of FR-4, since the microphone package is also made primarily of FR-4. These embodiments of the invention may also eliminate the need for wire bonding that is required in plastic body/lead frame packages. The footprint is typically smaller than that would be required for a plastic body/lead frame design since the leads may be formed by plating a through-hole in a circuit board to form the pathway to the solder pad. In a typical plastic body/lead frame design, a (gull wing configuration would be used in which the leads widen the overall foot print.

Now, referring to FIGS. 1-3, three embodiments of a silicon condenser microphone package 10 of the present invention are illustrated. Included within silicon microphone package 10 is a transducer 12, e.g. a silicon condenser microphone as disclosed in U.S. Pat. No. 5,870,482 which is hereby incorporated by reference and an amplifier 16. The package itself includes a substrate 14, a back volume or air cavity 18, which provides a pressure reference for the transducer 12, and a cover 20. The substrate 14 may be formed of FR-4 material allowing processing in circuit board panel form, thus taking advantage of economies of scale in manufacturing. FIG. 6 is a plan view of the substrate 14 showing the back volume 18 surrounded a plurality of terminal pads.

The back volume 18 may be formed by a number of methods, including controlled depth drilling of an upper surface 19 of the substrate 14 to form a recess over which the transducer 12 is mounted (FIG. 1); drilling and routing of several individual sheets of FR-4 and laminating the individual sheets to form the back volume 18, which may or may not have internal support posts (FIG. 2); or drilling completely through the substrate 14 and providing a sealing ring 22 on the bottom of the device that will seal the back volume 18 during surface mounting to a user's “board” 28 (FIGS. 3-5). In this example, the combination of the substrate and the user's board 28 creates the back volume 18. The back volume 18 is covered by the transducer 12 (e.g., a MEMS device) which may be “bumpbonded” and mounted face down. The boundary is sealed such that the back volume 18 is operably “air-tight.”

The cover 20 is attached for protection and processability. The cover 20 contains an aperture 24 which may contain a sintered metal insert 26 to prevent water, particles and/or light from entering the package and damaging the internal components inside; i.e. semiconductor chips. The aperture 24 is adapted for allowing sound waves to reach the transducer 12. The sintered metal insert 26 will also have certain acoustic properties, e.g. acoustic damping or resistance. The sintered metal insert 26 may therefore be selected such that its acoustic properties enhance the functional capability of the transducer 12 and/or the overall performance of the silicon microphone 10.

Referring to FIGS. 4 and 5 the final form of the product is a silicon condenser microphone package 10 which would most likely be attached to an end user's PCB 28 via a solder reflow process. FIG. 5 illustrates a method of enlarging the back volume 18 by including a chamber 32 within the end user's circuit board 28.

Another embodiment of a silicon condenser microphone package 40 of the present invention is illustrated in FIGS. 7-10. In this embodiment, a housing 42 is formed from layers of materials, such as those used in providing circuit boards. Accordingly, the housing 42 generally comprises alternating layers of conductive and non-conductive materials 44, 46. The non-conductive layers 46 are typically FR-4 board. The conductive layers 44 are typically copper. This multi-layer housing construction advantageously permits the inclusion of circuitry, power and ground planes, solder pads, ground pads, capacitance layers and plated through holes pads within the structure of the housing itself. The conductive layers provide EMI shielding while also allowing configuration as capacitors and/or inductors to filter input/output signals and/or the input power supply.

In the embodiment illustrated, the housing 42 includes a top portion 48 and a bottom portion 50 spaced by a side portion 52. The housing 42 further includes an aperture or acoustic port 54 for receiving an acoustic signal and an inner chamber 56 which is adapted for housing a transducer unit 58, typically a silicon die microphone or a ball grid array package (BGA). The top, bottom, and side portions 48, 50, 52 are electrically connected, for example with a conductive adhesive 60. The conductive adhesive may be provided conveniently in the form of suitably configured sheets of dry adhesive disposed between the top, bottom and side portions 48, 50 and 52. The sheet of dry adhesive may be activated by pressure, heat or other suitable means after the portions are brought together during assembly. Each portion may comprise alternating conductive and non-conductive layers of 44, 46.

The chamber 56 may include an inner lining 61. The inner lining 61 is primarily formed by conductive material. It should be understood that the inner lining may include portions of non-conductive material, as the conductive material may not fully cover the non-conductive material. The inner lining 61 protects the transducer 58 against electromagnetic interference and the like, much like a faraday cage. The inner lining 61 may also be provided by suitable electrically coupling together of the various conductive layers within the top, bottom and side portions 48, 50 and 52 of the housing.

In the various embodiments illustrated in FIGS. 7-10 and 23-26, the portions of the housing 42 that include the aperture or acoustic port 54 further include a layer of material that forms an environmental barrier 62 over or within the aperture 54. This environmental barrier 62 is typically a polymeric material formed to a film, such as a polytetrafluoroethylene (PTFE) or a sintered metal. The environmental barrier 62 is supplied for protecting the chamber 56 of the housing 42, and, consequently, the transducer unit 58 within the housing 42, from environmental elements such as sunlight, moisture, oil, dirt, and/or dust. The environmental barrier 62 will also have inherent acoustic properties, e.g. acoustic damping/resistance. Therefore the environmental barrier 62 is chosen such that its acoustic properties cooperate with the transducer unit 58 to enhance the performance of the microphone. This is particularly true in connection with the embodiments illustrated in FIGS. 24 and 25, which may be configured to operate as directional microphones.

The environmental barrier layer 62 is generally sealed between layers of the portion, top 48 or bottom 50 in which the acoustic port 54 is formed. For example, the environmental barrier may be secured between layers of conductive material 44 thereby permitting the layers of conductive material 44 to act as a capacitor (with electrodes defined by the metal) that can be used to filter input and output signals or the input power. The environmental barrier layer 62 may further serve as a dielectric protective layer when in contact with the conductive layers 44 in the event that the conductive layers also contain thin film passive devices such as resistors and capacitors.

In addition to protecting the chamber 56 from environmental elements, the barrier layer 62 allows subsequent wet processing, board washing of the external portions of the housing 42, and electrical connection to ground from the walls via thru hole plating. The environmental barrier layer 62 also allows the order of manufacturing steps in the fabrication of the printed circuit board-based package to be modified. This advantage can be used to accommodate different termination styles. For example, a double sided package can be fabricated having a pair of apertures 54 (see FIG. 25), both including an environmental barrier layer 62. The package would look and act the same whether it is mounted face up or face down, or the package could be mounted to provide directional microphone characteristics. Moreover, the environmental barrier layer 62 may also be selected so that its acoustic properties enhance the directional performance of the microphone.

Referring to FIGS. 7, 8, and 11-13 the transducer unit 58 is generally not mounted to the top portion 48 of the housing. This definition is independent of the final mounting orientation to an end user's circuit board. It is possible for the top portion 48 to be mounted face down depending on the orientation of the transducer 58 as well as the choice for the bottom portion 50. The conductive layers 44 of the top portion 48 may be patterned to form circuitry, ground planes, solder pads, ground pads, capacitors and plated through hole pads. Referring to FIGS. 1-13 there may be additional alternating conductive layers 44, non-conductive layers 46, and environmental protective membranes 62 as the package requires. Alternatively, some layers may be deliberately excluded as well. The first non-conductive layer 46 may be patterned so as to selectively expose certain features on the first conductive layer 44.

FIG. 11 illustrates an alternative top portion 48 for a microphone package. In this embodiment, a connection between the layers can be formed to provide a conduit to ground. The top portion of FIG. 11 includes ground planes and/or pattern circuitry 64 and the environmental barrier 62. The ground planes and or pattern circuitry 64 are connected by pins 65.

FIG. 12 illustrates another embodiment of a top portion 48. In addition to the connection between layers, ground planes/pattern circuitry 64, and the environmental barrier 62, this embodiment includes conductive bumps 66 (e.g. Pb/Sn or Ni/Au) patterned on the bottom side to allow secondary electrical contact to the transducer 58. Here, conductive circuitry would be patterned such that electrical connection between the bumps 66 and a plated through hole termination is made.

FIG. 13 illustrates yet another embodiment of the top portion 48. In this embodiment, the top portion 48 does not include an aperture or acoustic port 54.

Referring to FIGS. 7, 8 and 14-18, the bottom portion 50 is the component of the package to which the transducer 58 is primarily mounted. This definition is independent of the final mounting orientation to the end user's circuit board. It is possible for the bottom portion 50 to be mounted facing upwardly depending on the mounting orientation of the transducer 58 as well as the choice for the top portion 48 construction. Like the top portion 48, the conductive layers 44 of the bottom portion 50 may be patterned to form circuitry, ground planes, solder pads, ground pads, capacitors and plated through hole pads. As shown in FIGS. 14-18, there may be additional alternating conductive layers 44, non-conductive layers 46, and environmental protective membranes 62 as the package requires. Alternatively, some layers may be deliberately excluded as well. The first non-conductive layer 46 may be patterned so as to selectively expose certain features on the first conductive layer 44.

Referring to FIGS. 14 a through 14 d, the bottom portion 50 comprises a laminated, multi-layered board including layers of conductive material 44 deposited on layers of non-conductive material 46. Referring to FIG. 14 b, the first layer of conductive material is used to attach wire bonds or flip chip bonds. This layer includes etched portions to define lead pads, bond pads, and ground pads. The pads would have holes drilled through them to allow the formation of plated through-holes.

As shown in FIG. 14 c, a dry film 68 of non-conductive material covers the conductive material. This illustration shows the exposed bonding pads as well as an exposed ground pad. The exposed ground pad would come in electrical contact with the conductive epoxy and form the connection to ground of the side portion 52 and the base portion 50.

Referring to FIG. 14 d, ground layers can be embedded within the base portion 50. The hatched area represents a typical ground plane 64. The ground planes do not overlap the power or output pads, but will overlap the transducer 58.

Referring to FIG. 15, an embodiment of the bottom portion 50 is illustrated. The bottom portion 50 of this embodiment includes a solder mask layer 68 and alternating layers of conductive and non-conductive material 44, 46. The bottom portion further comprises solder pads 70 for electrical connection to an end user's board.

FIGS. 16 and 17 illustrate embodiments of the bottom portion 50 with enlarged back volumes 18. These embodiments illustrate formation of the back volume 18 using the conductive/non-conductive layering.

FIG. 18 shows yet another embodiment of the bottom portion 50. In this embodiment, the back portion 50 includes the acoustic port 54 and the environmental barrier 62.

Referring to FIGS. 7-10 and 19-22, the side portion 52 is the component of the package that joins the bottom portion 50 and the top portion 48. The side portion 52 may include a single layer of a non-conductive material 46 sandwiched between two layers of conductive material 44. The side portion 52 forms the internal height of the chamber 56 that houses the transducer 58. The side portion 52 is generally formed by one or more layers of circuit board material, each having a routed window 72 (see FIG. 19).

Referring to FIGS. 19-22, the side portion 52 includes inner sidewalls 74. The inner sidewalls 74 are generally plated with a conductive material, typically copper, as shown in FIGS. 20 and 21. The sidewalls 74 are formed by the outer perimeter of the routed window 72 and coated/metallized with a conductive material.

Alternatively, the sidewalls 74 may be formed by may alternating layers of non-conductive material 46 and conductive material 44, each having a routed window 72 (see FIG. 19). In this case, the outer perimeter of the window 72 may not require coverage with a conductive material because the layers of conductive material 44 would provide effective shielding.

FIGS. 23-26 illustrate various embodiments of the microphone package 40. These embodiments utilize top, bottom, and side portions 48, 50, and 52 which are described above. It is contemplated that each of the top, bottom, and side portion 48, 50, 52 embodiments described above can be utilized in any combination without departing from the invention disclosed and described herein.

In FIG. 23, connection to an end user's board is made through the bottom portion 50. The package mounting orientation is bottom portion 50 down. Connection from the transducer 58 to the plated through holes is be made by wire bonding. The transducer back volume 18 is formed by the back hole (mounted down) of the silicon microphone only. Bond pads, wire bonds and traces to the terminals are not shown. A person of ordinary skilled in the art of PCB design will understand that the traces reside on the first conductor layer 44. The wire bonds from the transducer 58 are be connected to exposed pads. The pads are connected to the solder pads via plated through holes and traces on the surface.

In FIG. 24, connection to the end user's board is also made through the bottom portion 50. Again, the package mounting orientation is bottom portion 50. Connection from the transducer 58 to the plated through holes are made by wire bonding. The back volume is formed by a combination of the back hole of the transducer 58 (mounted down) and the bottom portion 50.

In FIG. 25, connection to the end user's board is also made through the bottom portion 50. Again, the package mounting orientation is bottom portion 50. Connection from the transducer 58 to the plated through holes are made by wire bonding. With acoustic ports 54 on both sides of the package, there is no back volume. This method is suitable to a directional microphone.

In FIG. 26, connection to the end user's board is made through the top portion 48 or the bottom portion 53. The package mounting orientation is either top portion 48 down or bottom portion 50 down. Connection from the transducer 58 to the plated through holes is made by flip chipping or wire bonding and trace routing. The back volume 18 is formed by using the air cavity created by laminating the bottom portion 50 and the top portion 48 together. Some portion of the package fabrication is performed after the transducer 58 has been attached. In particular, the through hole formation, plating, and solder pad definition would be done after the transducer 58 is attached. The protective membrane 62 is hydrophobic and prevents corrosive plating chemistry from entering the chamber 56.

Referring to FIGS. 27-29, the portion to which the transducer unit 58 is mounted may include a retaining ring 84. The retaining ring 84 prevents wicking of an epoxy 86 into the transducer 58 and from flowing into the acoustic port or aperture 54. Accordingly, the shape of the retaining ring 84 will typically match the shape of the transducer 58 foot print. The retaining ring 84 comprises a conductive material (e.g., 3 mil. thick copper) imaged on a non-conductive layer material.

Referring to FIG. 27, the retaining ring 84 is imaged onto a nonconductive layer. An epoxy is applied outside the perimeter of the retaining ring 84, and the transducer 58 is added so that it overlaps the epoxy 86 and the retaining ring 84. This reduces epoxy 86 wicking up the sides of the transducer's 58 etched port (in the case of a silicon die microphone).

Alternatively, referring to FIG. 28, the retaining ring 84 can be located so that the transducer 58 does not contact the retaining ring 84. In this embodiment, the retaining ring 84 is slightly smaller than the foot print of the transducer 58 so that the epoxy 86 has a restricted path and is, thus, less likely to wick. In FIG. 29, the retaining ring 84 is fabricated so that it contacts the etched port of the transducer 58. The following tables provide an illustrative example of a typical circuit board processing technique for fabrication of the housing of this embodiment.

Table 1: Materials

TABLE 1 Materials Material Type Component Note 1 0.5/0.5 oz. DST Bottom Portion (Conductive Cu 5 core FR-4 Layers Non-Conductive Layer 1) 2 0.5/0.5 oz. DST Bottom Portion (Conductive Cu 5 core FR-4 Layers 3 and 4; Non- Conductive Layer 2) 3 106 pre-preg For Laminating Material 1 and Material 2 4 0.5/0.5 oz. DST Side Portion Metallized Cu 40 Core FR-4 Afterward 5 Bare/0.5 oz. Cu 2 Top Portion (Each Piece core FR-4 (2 Includes 1 Conductive and 1 pieces) Non-Conductive Layer) 6 Expanded PTFE Environmental Barrier

TABLE 2 Processing of Materials (Base Portion Material 1) Step Type Description Note 1 Dry Film Conductive Layers 2 Expose Mask Material 1 (Upper Forms Ground Conductive Layer) Plane on Lower Conductive Layer 3 Develop 4 Etch Cu No Etching on Upper Conductive Layer 5 Strip Dry Film

TABLE 3 Processing of Materials (Bottom Portion Material 2) Step Type Description Note 1 Dry Film Conductive Layers 2 Expose Mask Material 2 (Upper Forms Ground Conductive Layer) Plane on Upper Conductive Layer 3 Develop 4 Etch Cu No Etching on Upper Conductive Layer 5 Strip Dry Film

TABLE 4 Processing of Materials 1, 2, and 3 (Form Bottom Portion) Step Type Description Note 1 Laminate Materials 1 and 2 Laminated Using Material 3 2 Drill Thru Holes Drill Bit = 0.025 in. 3 Direct Plates Thru Holes Metallization/Flash Copper 4 Dry Film (L1 and L4) 5 Expose Mask Laminated Forms Traces and Solder Materials 1 and 2 Pads (Upper and Lower Conductive Layers) 6 Develop 7 Electrolytic Cu 1.0 mil 8 Electrolytic Sn As Required 9 Strip Dry Film 10 Etch Cu 11 Etch Cu 12 Insert Finishing NG Option (See NG Option for Proof Option Here Table Below) of Principle 13 Dry Film (cover 2.5 mil Minimum Thickness lay) on Upper on Upper Conductive Conductive Layer Layer Only 14 Expose Mask Laminated This mask defines an Materials 1 and 2 area on the upper (upper and lower) conductive layer that will receive a dry film solder mask (cover lay). The bottom layer will not have dry film applied to it. The plated through holes will be bridged over by the coating on the top. 15 Develop 16 Cure Full Cure 17 Route Panels Route Bit = As Forms 4″ × 4″ pieces. Required Conforms to finished dims

Table 5 describes the formation of the side portion 52. This process involves routing a matrix of openings in FR-4 board. However, punching is thought to be the cost effective method for manufacturing. The punching may done by punching through the entire core, or, alternatively, punching several layers of no-flow pre-preg and thin core c-stage which are then laminated to form the wall of proper thickness.

After routing the matrix, the board will have to be electroless or DM plated. Finally, the boards will have to be routed to match the bottom portion. This step can be done first or last. It may make the piece more workable to perform the final routing as a first step. Table 5: Processing of Material 4 (Side Portion)

TABLE 5 Processing of Material 4 (Side Portion) Step Type Description Note 1 Route/Punch Route Bit = 0.031 in. Forms Side Portion Matrix of Openings 2 Direct 0.25 mil minimum Forms Sidewalls Metallization/ on Side Portion Flash Cu 3 Route Panels

Table 6 describes the processing of the top portion. The formation of the top portion 48 involves imaging a dry film cover lay or liquid solder mask on the bottom (i.e. conductive layer forming the inner layer. The exposed layer of the top portion 48 will not have a copper coating. It can be processed this way through etching or purchased this way as a one sided laminate.

A matrix of holes is drilled into the lid board. Drilling may occur after the imaging step. If so, then a suitable solder mask must be chosen that can survive the drilling process.

TABLE 6 Processing of Top Portion Step Type Description Note 1 Dry Film Conductive Layer 2 Expose Mask Bare Layer Form Conduction Ring 3 Develop 4 Cure 5 Drill Matrix of Drill Bit 0.025 in. Acoustic Ports Holes 6 Laminate PTFE (Environmental Forms Top Portion Barrier) Between 2 Pieces of Material 5

TABLE 7 Processing of Laminated Materials 1 and 2 with Material 4 Step Type Description Note 1 Screen Conductive Adhesive on Material 4 2 Laminate Bottom Portion with Side Forms Bottom Portion Portion with Side Portion (spacer) 3 Add Transducer Silicon Die Microphone Assembly and Integrated Circuit

TABLE 8 Processing of Laminated Materials 1, 2, and 4 with Material 5 Step Type Description Note 1 Screen Conductive Adhesive on Top Portion 2 Laminate Bottom Portion and Side Forms Housing Portion with Top Portion 3 Dice

TABLE 9 Finishing Option NG (Nickel/Gold) Step Type Description Note 1 Immersion Ni (40-50 μ-in) 2 Immersion Au (25-30 μ-in)

TABLE 10 Finishing Option NGT (Nickel/Gold/Tin) Step Type 1 Mask L2 (using thick dry film or high tack dicing tape) 2 Immersion Ni (40-50 μ-in) 3 Immersion Au (25-30 μ-in) 4 Remove Mask on L2 5 Mask L1 (using thick dry film or high tack dicing tape) bridge over cavity created by wall 6 Immersion Sn (100-250 μ-in) 7 Remove Mask on L1

TABLE 11 Finishing Option ST (Silver/Tin) Step Type 1 Mask L2 (using thick dry film or high tack dicing tape) 2 Immersion Ag (40-50 μ-in) 3 Remove Mask on L2 4 Mask L1 (using thick dry film or high tack dicing tape) bridge over cavity created by wall 5 Immersion Sn (100-250 μ-in) 6 Remove Mask on L1

FIG. 30 is a plan view illustrating a panel 90 for forming a plurality of microphone packages 92. The microphone packages 92 are distributed on the panel 90 in a 14×24 array, or 336 microphone packages total. Fewer or more microphone packages may be disposed on the panel 90, or on smaller or larger panels. As described herein in connection with the various embodiments of the invention, the microphone packages include a number of layers, such as top, bottom and side portions of the housing, environmental barriers, adhesive layers for joining the portions, and the like. To assure alignment of the portions as they are brought together, each portion may be formed to include a plurality of alignment apertures 94. To simultaneously manufacture several hundred or even several thousand microphones, a bottom layer, such as described herein, is provided. A transducer, amplifier and components are secured at appropriate locations on the bottom layer corresponding to each of the microphones to be manufactured. An adhesive layer, such as a sheet of dry adhesive is positioned over the bottom layer, and a sidewall portion layer is positioned over the adhesive layer. An additional dry adhesive layer is positioned, followed by an environmental barrier layer, another dry adhesive layer and the top layer. The dry adhesive layers are activated, such as by the application of heat and/or pressure. The panel is then separated into individual microphone assemblies using known panel cutting and separating techniques.

The microphone, microphone package and method of assembly herein described further allow the manufacture of multiple microphone assembly, such as microphone pairs. In the simplest form, during separation two microphones may be left joined together, such as the microphone pair 96 shown in FIG. 31. Each microphone 98 and 100 of the microphone pair 96 is thus a separate, individually operable microphone in a single package sharing a common sidewall 102. Alternatively, as described herein, conductive traces may be formed in the various layers of either the top or bottom portion thus allowing multiple microphones to be electrically coupled.

While specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying Claims. 

What is claimed is:
 1. A method for manufacturing a plurality of solder reflow surface mount microelectromechanical system (MEMS) microphones, the method comprising: providing an unsingulated panel comprised of a plurality of individual rectangular substrates, each rectangular substrate comprising: a base layer comprised of at least one layer of non-conductive material, wherein the base layer has a planar top surface and a planar bottom surface, the top surface having an interior region and an attachment region, the attachment region disposed between the interior region and the edges of the base layer, and completely bounding the interior region; a first plurality of metal pads disposed on the top surface of the base layer; a second plurality of flat metal pads disposed on the bottom surface of the base layer, the second plurality of metal pads arranged to be within the edges of the bottom surface of the base layer; one or more electrical pathways disposed completely within the base layer, wherein the pathways electrically couple one or more of the first plurality of metal pads on the top surface of the base layer to one or more of the second plurality of metal pads on the bottom surface of the base layer; and an acoustic port disposed in the interior region of the base layer and passing completely through the base layer, wherein the acoustic port is disposed in a position offset from a centerpoint of the substrate, and wherein one of the second plurality of metal pads is a metal ring that completely surrounds the acoustic port in the base layer; mounting a MEMS microphone die to the top surface of each individual substrate in the panel of unsingulated substrates, and electrically coupling the MEMS microphone die to at least one of the first plurality of metal pads on the top surface of its respective substrate, the MEMS microphone die being disposed directly over the acoustic port in the base layer of its respective substrate; providing a plurality of single-piece rectangular covers, wherein each individual rectangular cover is formed from a solid material and has a top portion and a sidewall portion, the sidewall portion supporting the top portion and adjoining the top portion at a substantially perpendicular angle and having a predetermined height, an exterior surface, an interior surface, and an attachment surface; attaching a single-piece rectangular cover to each individual substrate on the panel of unsingulated substrates, one cover to each individual substrate, wherein the attachment surface of the sidewall portion of the cover is aligned with and attached to the attachment region of the top surface of its respective individual substrate, and wherein the predetermined height and interior surface of the sidewall portion of the cover and the interior surface of the top portion of the cover, in cooperation with the interior region of the top surface of its respective individual substrate, forms a protective enclosure for the MEMS microphone die to reduce electromagnetic interference and to define an acoustic chamber for the MEMS microphone die; and singulating the substrate panel into individual MEMS microphones.
 2. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual substrate in the panel of unsingulated substrates, the method further comprises electrically coupling at least one passive electrical element between one of the first plurality of metal pads and one of the second plurality of metal pads.
 3. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 2, wherein, for each individual substrate in the panel of unsingulated substrates, the at least one passive electrical element is disposed within the base layer of the individual substrate.
 4. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 3, wherein, for each individual substrate in the panel of unsingulated substrates, the at least one passive electrical element comprises a dielectric or resistive material that is different from the non-conductive material in the base layer of the individual substrate.
 5. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 2, wherein, for each individual substrate in the panel of unsingulated substrates, the at least one passive electrical element is configured to filter one or more of an input signal, an output signal, or input power.
 6. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual substrate in the panel of unsingulated substrates, the individual substrate further comprises an acoustic material that substantially blocks environmental contaminants from entering the acoustic chamber through the acoustic port.
 7. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 6, wherein, for each individual substrate in the panel of unsingulated substrates, the acoustic material is a film of polymeric material.
 8. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 6, wherein, for each individual substrate in the panel of unsingulated substrates, the acoustic material is hydrophobic.
 9. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual substrate in the panel of unsingulated substrates, the individual substrate further comprises a metal pad with an opening, wherein the opening surrounds the acoustic port in the base layer, and the metal pad is interposed between the MEMS microphone die and the top surface of the base layer.
 10. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual substrate in the panel of unsingulated substrates, the individual substrate further comprises a metal pad with an opening, wherein the opening surrounds the acoustic port in the base layer, and the MEMS microphone die contacts the metal pad when mounted on the top surface of the base layer.
 11. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual substrate in the panel of unsingulated substrates, the base layer comprises one or more layers of FR-4 printed circuit board material.
 12. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual microphone, the enclosure protects the MEMS microphone die from at least one of light and physical damage.
 13. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual microphone, a diaphragm of the MEMS microphone die defines a front volume and a back volume within the acoustic chamber, and the acoustic port disposed in the base layer of the substrate is acoustically coupled to the front volume.
 14. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 13, wherein, for each individual microphone, the interface between the attachment surface of the sidewall portion of the cover and the attachment region of the top surface of the substrate is sealed to maintain acoustic pressure within the back volume.
 15. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual microphone, the MEMS microphone die is a pressure-equalizing MEMS microphone die.
 16. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 1, wherein, for each individual microphone, the acoustic port in the base layer is a first acoustic port and the top portion of the rectangular cover further comprises a second acoustic port.
 17. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 16, wherein, after each individual rectangular cover is attached to its respective substrate in the unsingulated panel of substrates, its respective acoustic chamber acoustically couples the diaphragm of its respective MEMS microphone die to its respective second acoustic port.
 18. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 16, wherein, for each individual rectangular cover, the second acoustic port further comprises a barrier that substantially blocks contaminants from entering the acoustic chamber through the second acoustic port.
 19. A method for manufacturing a plurality of solder reflow surface mount microelectromechanical system (MEMS) microphones, the method comprising: providing an unsingulated patent of rectangular base portions, each individual rectangular base portion comprising: a base layer comprised of at least one layer of printed circuit board material, wherein the base layer has a substantially flat upper surface and a substantially flat lower surface, the upper surface having an inner area and a coupling area, the coupling area located between the inner area and the edges of the base layer, and completely surrounding the inner area; a plurality of metal pads located on the upper surface of the base layer; a plurality of flat solder pads located on the lower surface of the base layer, the plurality of solder pads arranged to be within the edges of the lower surface of the base layer; one or more electrical connections passing through the base layer, wherein the connections electrically couple one or more of the plurality of metal pads on the upper surface of the base layer to one or more of the plurality of solder pads on the lower surface of the base layer; an acoustic port located in the inner area of the base layer and passing completely through the base layer, wherein the acoustic port is disposed in a position offset from a centerpoint of the base portion, and wherein one of the second plurality of solder pads is a solder pad ring that completely surrounds the acoustic port in the base layer; and at least one passive electrical element disposed within the base layer and electrically coupled between one of the plurality of metal pads and one of the plurality of solder pads; mounting a MEMS microphone die to the upper surface of each individual base portion in the unsingulated panel of base portions, and electrically coupling each MEMS microphone die to at least one of the plurality of metal pads on the upper surface of the base layer of its respective base portion, wherein the MEMS microphone die being disposed directly over the acoustic port in the base layer of its respective base portion; and providing a plurality of individual rectangular cover portions, each rectangular cover portion formed from a single piece of solid material, and having a top portion and a sidewall portion, the sidewall portion supporting the top portion and adjoining the top portion at a substantially perpendicular angle and having a predetermined height, an exterior surface, an interior surface, and a coupling surface; coupling a rectangular cover portion to each individual base portion on the panel of unsingulated base portions, one cover portion to each individual base portion, wherein the coupling surface of the sidewall portion of the cover portion is aligned with and mechanically attached to the coupling area of the base layer of its respective base portion; wherein the predetermined height and interior surface of the sidewall portion of the cover position, and the interior surface of the top portion of the cover portion, in cooperation with the interior region of the upper surface of the base layer of respective base portion, forms a protective enclosure for the MEMS microphone die to define an acoustic chamber for the MEMS microphone die; and wherein the overall length of the base portion and cover portion are substantially equal, and the overall width of the base portion and cover portion are substantially equal; and singulating the panel of base portions into individual MEMS microphones.
 20. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 19, wherein, for each individual base portion in the panel of unsingulated base portions, each individual base portion further comprises a metal pad with an opening, wherein the opening surrounds the acoustic port in the base layer of the base portion, and the metal pad is interposed between the MEMS microphone die and the upper surface of the base layer of the base portion.
 21. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 19, wherein, for each individual MEMS microphone, the enclosure protects the MEMS microphone die from at least one of light, electromagnetic interference, and physical damage.
 22. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 19, wherein, for each individual base portion in the panel of unsingulated base portions, the base layer of each individual base portion further comprises an acoustic material that substantially blocks contaminants from entering the acoustic chamber through the acoustic port.
 23. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 22, wherein, for each individual base portion in the panel of unsingulated base portions, the acoustic material is a film of polymeric material.
 24. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 22, wherein, for each individual base portion in the panel of unsingulated base portions, the acoustic material is hydrophobic.
 25. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 19, wherein, for each individual MEMS microphone, a diaphragm of the MEMS microphone die defines a front volume and a back volume within the acoustic chamber, and the acoustic port disposed in the base layer of the base portion is acoustically coupled to the front volume; and wherein the interface between the coupling surface of the sidewall portion of the cover portion and the coupling area of the upper surface of the base layer of the base portion is sealed to maintain acoustic pressure within the back volume.
 26. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 19, wherein, for each individual microphone, the acoustic port of the base layer is a first acoustic port and the top portion of the rectangular cover portion further comprises a second acoustic port.
 27. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 19, wherein, for each individual base portion in the panel of unsingulated base portions, the at least one passive electrical element is disposed within the base layer of the base portion, wherein the at least one passive electrical element comprises a dielectric or resistive material that is different from the printed circuit board material in the base layer of the base portion.
 28. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 27, wherein, for each individual base portion in the panel of unsingulated base portions, the at least one passive electrical element is configured to filter one or more of an input signal, an output signal, or input power.
 29. A method for manufacturing a plurality of solder reflow surface mount microelectromechanical system (MEMS) microphones, the method comprising: providing an unsingulated panel comprising a plurality of rectangular base elements, each individual base element comprising: a core layer comprised of at least one layer of FR-4 printed circuit board material, wherein the core layer has a substantially flat top surface and a substantially flat bottom surface, the top surface having a die mount region and an attachment region, the attachment region positioned between the die mount region and the edges of the core layer, and completely surrounding the die mount region; a plurality of metal pads located on the top surface of the core layer; a plurality of flat solder pads located on the bottom surface of the core layer, the plurality of solder pads arranged to be within the edges of the bottom surface of the core layer, wherein the solder pads are plated with at least one metal; a plurality of electrical connections passing through the core layer that electrically couple one or more of the plurality of metal pads on the top surface of the core layer to one or more of the plurality of solder pads on the bottom surface of the core layer; an acoustic port located in the interior region of the core layer and passing completely through the core layer, wherein the acoustic port is disposed in a position offset from a centerpoint of the base element, and wherein one of the second plurality of solder pads is a solder pad ring that completely surrounds the acoustic port in the base element; and at least one passive electrical element disposed within the core layer and electrically coupled between one of the plurality of metal pads and one of the plurality of solder pads; and a pressure-equalizing MEMS microphone die having an internal acoustic channel mounted in the die mount region of the core layer, and electrically coupled to one or more of the metal pads on the top surface of the core layer, the internal acoustic channel of the MEMS microphone die being arranged directly over the acoustic port in the core layer; providing a plurality of single-piece rectangular cover elements, each rectangular cover element formed from a solid material and having a top region and a wall region, the wall portion supporting the top portion and wall region adjoining the top region at a substantially perpendicular angle and having a predetermined height, an exterior surface, an interior surface, and an attachment surface; coupling a rectangular cover element to each individual base element on the panel of unsingulated base elements, one cover element to each individual base element, wherein the cover element is attached to the base element such that the attachment surface of the wall region of the cover element is aligned with and physically coupled to the attachment region of the top surface of the core layer of its respective base element, thereby forming a protective enclosure for the MEMS microphone die, and wherein the interior of the protective enclosure is an acoustic chamber having a volume defined by the predetermined height of wall region of the cover element, and the width and length of the top region of the cover element; and singulating the panel of base elements into individual MEMS microphones.
 30. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 29, wherein, for each individual base element in the panel of unsingulated base elements, the at least one passive electrical element comprises a dielectric or resistive material that is different from the FR-4 printed circuit board material in the core layer of the base element.
 31. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 30, wherein, for each individual base element in the panel of unsingulated base elements, the at least one passive electrical element is configured to filter one or more of an input signal, an output signal, or input power.
 32. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 29, wherein, for each individual MEMS microphone, the enclosure protects the MEMS microphone die from at least one of light, electromagnetic interference, and physical damage.
 33. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 29, wherein, for each individual base element in the panel of unsingulated base elements, the core layer of the base element further comprises an acoustic material that substantially blocks contaminants from entering the acoustic chamber through the acoustic port.
 34. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 33, wherein, for each individual base element in the panel of unsingulated base elements, the acoustic material is a film of polymeric material.
 35. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 33, wherein, for each individual base element in the panel of unsingulated base elements, the acoustic material is hydrophobic.
 36. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 29, wherein, for each individual MEMS microphone, a diaphragm of the MEMS microphone die defines a front volume and a back volume within the acoustic chamber, and the acoustic port disposed in the core layer of the base element is acoustically coupled to the front volume; and wherein the interface between the attachment surface of the wall region of the cover element and the attachment area of the top surface of the core layer of the base element is sealed to maintain acoustic pressure within the back volume.
 37. A method for manufacturing a plurality of solder reflow surface mount microelectromechanical system (MEMS) microphones, the method comprising: providing a plurality of a pressure-equalizing MEMS microphone die, each having an internal acoustic channel; providing an unsingulated panel comprising a plurality of first housing elements each having a rectangular shape, the first housing elements further comprising: a core layer comprised of multiple layers of FR-4 printed circuit board material, wherein the core layer has a substantially flat top surface and a substantially flat bottom surface, wherein the top surface has an die mount region and an attachment region, the attachment region being arranged between the die mount region and the edges of the core layer, and the attachment region completely surrounds the die mount region; a plurality of metal pads disposed on the top surface of the core layer, wherein the metal pads are plated with at least one metal; a plurality of flat solder pads disposed on the bottom surface of the core layer, the plurality of solder pads arranged to be within a perimeter of the bottom surface of the core layer, wherein the solder pads are plated with at least one metal; one or more electrical vias located inside the core layer, wherein the vias electrically couple one or more of the plurality of metal pads on the top surface of the core layer to one or more of the plurality of solder pads on the bottom surface of the core layer; an acoustic port located in the die mount region of the core layer and passing completely through the core layer, wherein the acoustic port is disposed in a position offset from a centerpoint of the first housing element, and wherein one of the plurality of solder pads is a solder pad ring that completely surrounds the acoustic port in the core layer; and at least one passive electrical element disposed within the core layer and electrically coupled between one of the plurality of metal pads and one of the plurality of solder pads, wherein the at least one passive electrical element comprises a dielectric or resistive material that is different from the printed circuit board material in the core layer; providing a plurality of second housing elements each having a rectangular shape, each second housing element formed from a single piece of solid material, and having a top region and a wall region, the wall portion supporting the top portion and wall region adjoining the top region at a substantially perpendicular angle and having a predetermined height, an exterior surface, an interior surface, and an attachment surface; coupling a MEMS microphone die to each first housing element in the unsingulated panel of first housing elements, wherein each MEMS microphone die is disposed in the die mount region of the core layer of its respective first housing element, and electrically coupled to one or more of the metal pads on the top surface of the core layer of its respective first housing element, the internal acoustic channel of the MEMS microphone die being arranged directly over the acoustic port in the core layer in its respective first housing element; forming a protective housing for each MEMS microphone die mounted on a first housing element in the unsingulated panel of first housing elements by coupling a second housing element to each first housing element in the unsingulated panel of first housing elements, wherein the attachment surface of the wall region of the second housing element is aligned with and physically coupled to the attachment region of the top surface of the core layer of the first housing element, thereby forming a protective enclosure for the MEMS microphone die, and wherein the interior of the protective enclosure is an acoustic chamber having a volume defined by the predetermined height of wall region of the second housing element, and the width and length of the top region of the second housing element; and singulating the panel of first housing elements into individual MEMS microphones.
 38. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 37, wherein, for each individual MEMS microphone, the enclosure protects the MEMS microphone die from at least one of light, electromagnetic interference, and physical damage.
 39. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 37, wherein, for each first housing element in the unsingulated panel of first housing elements, the core layer of the first housing element further comprises an acoustic material that substantially blocks contaminants from entering the acoustic chamber through the acoustic port.
 40. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 39, wherein, for each first housing element in the unsingulated panel of first housing elements, the acoustic material is a film of polymeric material.
 41. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 39, wherein, for each first housing element in the unsingulated panel of first housing elements, the acoustic material is hydrophobic.
 42. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 37, wherein, for each individual microphone, the acoustic port in the core layer of the first housing element is a first acoustic port and the top portion of the second housing element further comprises a second acoustic port.
 43. A method for manufacturing a plurality of surface mount MEMS microphones according to claim 37, wherein, for each first housing element in the unsingulated panel of first housing elements, the at least one passive electrical element is configured to filter one or more of an input signal, an output signal, or input power. 